A network can be defined as the interconnection of various devices, referred to herein as nodes. Whenever there are multiple nodes transmitting on the same radio frequency, there is a likelihood that two or more nodes will transmit at the same time, causing a collision. The Medium Access Control (MAC) layer deals with the problem of how to control access to the shared channel. Some of the well-known methods of media access control include Pure ALOHA, Slotted ALOHA, Persistent and Nonpersistent Carrier Sense Multiple Access (CSMA).
In some cases, each node in a network can hear transmissions from all other nodes. Nodes will then refrain from transmitting data when other nodes are transmitting. Whether the nodes are trying to use the media is most often determined by detecting the carrier of the one or more transmitting nodes.
In other cases, however, each node in a network can only hear transmissions from its neighbor nodes. Some media access control protocols teach the partitioning of the communication bandwidth into frames that are divided into media access slots, where some slots are reserved as a beacon period and remaining slots are used for data transmission.